VEGETABLE CELLS IN GENERAL. PROTOPHYTES. 243 



in local aggregations, leaving parts of the protoplasm unco'oured. 

 The superficial layer, in particular, is frequently destitute of 

 colour; and the Primordial Utricle appears to be formed by its 

 solidification. In the interior of the viscid mass, are commonly 

 found Vacuoles, which are distinguished from the surrounding 

 substance by their difference in refracting power ; these, however, 

 are not usually void spaces, but are cavities in the Protoplasm 

 occupied by fluid of a more watery consistence ; and this ' vacuola- . 

 tion ' of the interior, which increases until the cell-contents have 

 almost entirely lost their original viscidity and are of a more 

 watery character, seems to take-place pari passu with the consoli- 

 dation of the exterior into distinct membranous walls ; so that the 

 development of a perfect Cell out of a rudimentary mass of Endo- 

 chrome may be stated to consist essentially in the gradual differen- 

 tiation of its substance, which was at first a nearly homogeneous 

 viscid mass, into the solid Cell -wall and the liquid Cell-contents. 

 — (See also § 286.) 



i84. Now among the Protophyles or simplest Plants, on the 

 examination of which we are about to enter, there are many or 

 which every single Cell is not only capable of living in a state of 

 isolation from the rest, but even normally does so ; and thus, in 

 the ordinary phraseology, every Cell is to be accounted a ' distinct 

 individual.' There are others, again, of which shapeless masses 

 are made up by the aggregation of contiguous Cells, which, though 

 quite capable of living independently, remain attached to each 

 other by the mutual fusion (so to speak) of their gelatinous invest- 

 ments. And there are others, moreover, in which a definite adhe- 

 sion exists between the Cells, and in which regular plant-like struc- 

 tures are thus formed, notwithstanding that every cell is still but 

 a repetition of every other, and is capable of living independently 

 if detached, so as to answer to the designation of a Unicellular 

 or single-celled Plant. These different conditions we shall find to 

 arise out of the mode in which each particular species multiplies 

 by binary subdivision (§ 185) : for where the cells of the new pair 

 that is produced by the segmentation of the previous cell undergo 

 a complete separation from one another, they will henceforth live 

 quite separately ; but if, instead of undergoing this complete fusion, 

 they should be held-together by the intervening gelatinous envelope, 

 a shapeless mass results from repeated subdivisions not taking 

 place on any determinate plan ; and if, moreover, the binary 

 subdivision should always take-place in a determinate direction, a 

 long narrow filament (Fig. 147 d), or a broad flat leaf -like ex- 

 pansion (g), may be generated. To such extended fabrics the 

 term Unicellular Plants can scarcely be applied with propriety ; 

 since they may be built-up of many thousands or millions of dis- 

 tinct Cells, which have no disposition to separate from each other 

 spontaneously. Still they correspond with those which are strictly 

 Unicellular, as to the absence of differentiation either in struc- 



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